In many industrial environments, heavy equipment requires manual manipulation and operation on a workpiece. By way of example, but not limitation, tools used for fitting, preparing, and repairing large pipes in any of a variety of environments are typically manually operated by individuals and, because of their weight, operating torque, and the like, are occasionally given to disengagement from the workpiece, with the result being an extremely heavy piece of equipment dropping to the floor or ground. This becomes extremely dangerous to personnel and hazardous to the equipment itself, particularly when working with heavy equipment in overhead locations. One particular type of equipment for which such problems exist is a pipe end prep tool, which may weigh in excess of 600 lbs., and which typically requires the clamping of the tool to the inside diameter or circumference of a pipe, while milling blades operate on the end of the tool to dress and finish it for coupling or fitting it to another pipe or repair piece.
When clamping a pipe end prep tool to the inside diameter or circumference of a pipe, it is necessary for the tool to center on the pipe inside diameter in order to ensure that the preparation and finishing of the pipe end is square to the pipe outside diameter. In order to accomplish this, it is necessary that the operator be able to shake or rock the pipe end pre tool to ensure that the internal clamps expand in a uniform manner as they move up on a tapered mandrel and engage the inside pipe diameter or circumference. If it is not possible to shake or rock the pipe end prep tool as the clamps tighten on the pipe internally, the tool could easily be cocked off center or at an angle with the end result being a preparation of the end of the pipe that is not square to the pipe outside diameter.
While smaller tools, which are generally lighter and easier to handle, allow the operator to simply shake or rock them as the clamps engage the interior of the pipe, heavier pipe end prep tools, which may weigh over 600 lbs., render such shaking and rocking impractical, if not impossible. To overcome this problem, the art has employed drawbar springs to offset the weight of the pipe end prep tool and allow the operator to shake or rock it easily. The drawbar springs, attached at a fixed location above the tool and connected to the tool, support a significant portion of the weight of the tool and give the operator the perceptible feel of the pipe end prep tool squaring itself to the outside diameter as the clamps move up the tapered mandrel and tighten to the inside diameter of the pipe.
While drawbar springs do facilitate the handling and manipulation of such heavy tools, they have been found to break and come apart if the springs are allowed to bottom out by extending to their maximum load limit. The braking of a spring or springs results in the pipe end prep tool unexpectedly dropping, risking injury to personnel, other equipment, and the tool itself.